Microsoft 365 Alert – Service Degradation – Exchange Online – Users may be unable to open Excel files attached to email messages in new Outlook and receive an error – ONGOING

Announcements Arpan Das

28/11/2025 08:51:00 AM

NHSmail Reference: INC46693238

Microsoft Reference: EX1189359

Issue Status: ONGOING

Issue Description: Users may be unable to open Excel files attached to email messages in new Outlook and receive an error

More info: Users receive an error stating: “Try opening the file again later.”

This issue impacts attachments that contain non-ASCII characters. As a way to avoid impact, users can utilize Outlook on the web or download the file locally to manually open Excel files.

Current Update: 05/12/2025 08:22:00 AM – Microsoft have completed validations and have begun deploying the fix to the affected environment. The saturation is currently at 30 percent, and they are monitoring as it progresses to ensure it completes in a timely manner.

Scope of impact: Any user may be unable to open Excel files attached to email messages in the new Outlook client if the attachment contains non-ASCII characters.

Root cause: An encoding error within Excel file names is resulting in this impact.

Next update by: Friday, December 5, 2025, at 10:00 PM UTC